As a mounting technology for a semiconductor chip, a flip chip technology, by which a semiconductor chip is directly connected onto a substrate has been known. In the flip chip mounting, a semiconductor chip and a circuit substrate are connected by means of electrodes (bumps) formed on the element formation surface side of the semiconductor chip. On this occasion, for the sake of reinforcement of the bonding parts and enhancement of the reliability of the connections, an underfill sealant, which is an adhesive composition, is generally filled between the semiconductor chip and the wiring substrate.
As an underfill composition, adhesive compositions containing an epoxy-based compound and/or a (meth)acrylic compound or the like have been known (e.g. Japanese Patent Laid-Open No. 2010-226098). Among them, a composition utilizing a radical curing reaction of a (meth)acrylic compound has an advantage over a composition containing an epoxy-based compound that the reaction rate is higher and the efficiency in producing an electronic device can be enhanced.
Meanwhile, various additives, such as an antioxidant and a metal ion binder, are mixed as needed, into an underfill composition. By this means, the quality of an electronic device can be enhanced by, for example, improving mechanical strength, adhesiveness, a rate of cross-linking and the like (Japanese Patent Laid-Open No. H08 (1996)-213517).
As a method for filling an underfill sealant, it has been known that a method in which a liquid adhesive composition is first applied on a wiring substrate and then a semiconductor chip is mounted to conduct simultaneously electrode connection and sealing; a method (a so-called capillary method) in which electrical connection between an electrode on a semiconductor chip and a substrate is first established and then a liquid adhesive composition is applied on a side or a plurality of sides of the chip for sealing the gap between the wiring substrate and the semiconductor chip by capillarity and the like. By any of the methods, it is required to apply a liquid adhesive composition all over the wiring substrate, to fill the liquid adhesive composition uniformly in the gap between the semiconductor chip and the wiring substrate, and the like. Therefore, occasionally, a syringe, the substrate and the like are heated to room temperature or higher as needed in order to increase flowability of the adhesive composition.
However, when an underfill sealant utilizing a radical curing reaction is used, there has been a problem in that a curing reaction of an underfill sealant composition may occasionally progress prematurely before carrying out sealing, which leads to inadequate electrode connection or poor work efficiency. Such a problem tends to occur when an adhesive composition is in a state at room temperature or higher, as described above. In order to overcome the problem, whereas an additive is mixed in an underfill sealant composition or the working temperature is lowered, it has not been sufficient. Consequently, further improvement of an adhesive composition to be used for an electronic device has been sought after.